For architectural flat glass, such as is made by the "float" process, two of the more prominent techniques for creating solar management coatings on these glasses are the pyrolytic process and the magnetron sputter coating process. Drawbacks heretofore experienced in the sputter coating process have been that the coatings can often be easily rubbed off (i.e. lack durability) and that the polysealant used in forming multi-paned architectural windows often attacks the coating. This, in turn, breaks down the seal between the panes, allowing detrimental condensation to accumulate between them. On the other hand, sputter coatings have had the historic advantage of being able to achieve low emissivity values and high visible light transmittance properties, as compared to most pyrolytic coatings. These latter two properties are perhaps among the most important to achieve in certain architectural glasses.
The terms "emissivity" and "transmittance" are well understood in the art and are used herein according to their well known meaning. Thus, for example, the term "transmittance" herein means solar transmittance, which is made up of visible light transmittance, infrared energy transmittance, and ultraviolet light transmittance. Total solar energy transmittance is then usually characterized as a weighted average of these other values. With respect to these transmittances, visible transmittance, as reported herein, is characterized by the standard Illuminant C (10.degree. obs., unless otherwise specified) technique at 380-720 nm; infrared is 800-2100 nm; ultraviolet 300-400 nm; and total solar is 300-2100 nm. For purposes of emissivity, however, a particular infrared range (i.e. 2,500-40,000 nm) is employed, as discussed below.
Visible transmittance can be measured using known, conventional techniques. For example, by using a spectrophotometer, such as a Beckman 5240 (Beckman Sci. Inst. Corp.), a spectral curve of transmission at each wavelength is obtained. Visible transmission is then calculated using ASTM E-308 "Method for Computing the Colors of Objects by Using the CIE System" (Annual Book of ASTM Standards, Vol. 14.02). A lesser number of wavelength points may be employed than prescribed, if desired. Another technique for measuring visible transmittance is to employ a spectrometer such as a commercially available Spectragard spectrophotometer manufactured by Pacific Scientific Corporation. This device measures and reports visible transmittance directly.
"Emissivity" (E) is a measure, or characteristic of both absorption and reflectance of light at given wavelengths. It is usually represented by the formula: EQU E=1-Reflectance.sub.film
For architectural purposes, emissivity values become quite important in the so-called "mid range", sometimes also called the "far range", of the infrared spectrum, i.e. about 2,500-40,000 nm The term "emissivity" as used herein, is thus used to refer to emissivity values measured in this infrared range as specified by the 1991 Proposed ASTM Standard for measuring infrared energy to calculate emittance, as proposed by the Primary Glass Manufacturers'Council and entitled "Test Method for Measuring and Calculating Emittance of Architectural Flat Glass Products Using Radiometric Measurements". This Standard, and its provisions, are incorporated herein by reference. In this Standard, hemispherical emissivity (F.sub.h) can be broken down into components, one of which is its normal emissivity (E.sub.n) component.
The actual accumulation of data for measurement of such emissivity values is conventional and may be done by using, for example, a Beckman Model 4260 spectrophotometer with "VW" attachment (Beckman Scientific Inst. Corp.). This spectrophotometer measures reflectance versus wavelength (i.e. normal emittance, E.sub.n), and from this, hemispherical emissivity (E.sub.h) is calculated using the aforesaid 1991 Proposed ASTM Standard which has been incorporated herein by reference.
Another term employed herein is "sheet resistance". Sheet resistance (R.sub.s) is a well known term in the art and is used herein in accordance with its well known meaning. Generally speaking, this term refers to the resistance in ohms for any square of a layer system on a glass substrate to an electric current passed through the layer system. Sheet resistance is an indication of how well the layer is reflecting infrared energy, and is thus often used along with emissivity as a measure of this characteristic, so important in many architectural glasses. "Sheet resistance" is conveniently measured by using a 4-point probe ohmmeter, such as a 4-point resistivity probe with a Magnetron Instruments Corp. head, Model M-800 produced by Signatone Corp. of Santa Clara, Calif.
As stated above, for many architectural purposes it is desirable to have as low an emissivity and R.sub.s as feasible, such that the glass window is reflecting substantial amounts of the infrared energy impinging on the glass. Generally speaking, "low E" (i.e. low emissivity) glasses are considered to be those glasses which have a hemispherical emissivity (E.sub.h) of less than about 0.16 and a normal emissivity (E.sub.n) of less than about 0.12. At the same time, sheet resistance (R.sub.s) is, therefore, preferably less than about 12 ohms/sq. Such glasses, to be commercially acceptable, usually are required to transmit as much visible light as possible, often about 76% or more using the Illuminant C technique for measuring transmittance in glasses of about 2 mm-6 mm thick.
"Chemical resistance" herein is determined by boiling a 2".times.5" sample of the article in about 500 cc of 5% HCl for one hour (i.e. about 220.degree. F.). The article is deemed to pass this test if it shows no pinholes greater than about 0,003" in diameter after this one hour boil.
"Durability" is herein measured by one of two tests, first a conventional Taber abrader test using a 4".times.4" sample and a 500 g weight attached to each of two C.S. 10F. abrasion wheels rotated through 100-300 revolutions. Durability may also be tested using a Pacific Scientific Abrasion Tester (1"nylon brush cyclically passed over the coating in 500 cycles employing 150 gms. of weight, applied to a 6".times.17"sample). In both tests, if no substantially noticeable scratches appear when viewed with the naked eye under visible light, the test is deemed passed, and the article is said to be durable. A less subjective evaluation may be made by measuring the change in visible transmission between the unabraded portion of the sample with the abraded portion and placing a numerical value (e.g. percent reduction) on any decrease in the transmission. By placing a numerical limit on the decrease, a "pass" or "fail" mark can be established (e.g. "more than 20%" would be one limit that might be set).
The term "heat-treatable" is used in this invention differently than in our former patents and applications in the following respect. In both this invention and our former patents, etc. the term assumed (and still assumes) that an acceptable product by way of uniformity (as well as chemical and mechanical durability in preferred embodiments) is achieved after heat-treatment. In our former patents, etc., it was also desired in their preferred embodiments that the solar management properties (including color) not be materially changed during heat-treatment. In this invention, on the other hand, the term "heat-treatable" does not necessarily include such a restriction, since in some embodiments it may well be desirable that the solar management properties change significantly in order to match the characteristics of another (e.g. unheat-treated) product with which it is to be matched. In this invention, however, the ultimate solar management properties are to be those predetermined and desired. Of course, the heat-treatment must also not adversely affect, to any substantial extent, the uniformity (and/or mechanical and chemical durability characteristics in preferred embodiments) of the product before heat-treatment (except to the extent that the heat-treatment may improve such characteristics).
The technique of creating architectural glass by magnetron sputter coating multiple layers of metals and/or metal oxides or nitrides onto float glass sheets is well known and a large number of permutations and combinations of known metals (e.g. Ag, Au, etc.), oxides and nitrides (including Si.sub.3 N.sub.4) have been attempted and reported. Such techniques may employ either planar or tubular targets, or a combination of both, and multi-target zones to achieve their desired results. Exemplary of preferred apparatus for use in this invention, and known in the art, is a magnetron sputter coater sold by Airco Corporation. This commercially available device is disclosed in U.S. Pat. Nos. 4,356,073 and 4,422,916, respectively. The disclosures of these patents are incorporated herein by reference.
In particular, it has been known to use the aforesaid Airco sputter coater to produce architectural glasses having a layering system, sequentially from the glass (e.g. standard float glass) outwardly, as follows: EQU Si.sub.3 N.sub.4 /Ni:Cr/Ag/Ni:Cr/Si.sub.3 N.sub.4
in which it has been found in practice that the Ni:Cr alloy is 80/20 by weight Ni/Cr, respectively (i.e. nichrome), and wherein the two nichrome layers are reported as being about 7 .ANG. thick, the Ag layer is specified as being about 70 .ANG. thick (except that it is stated that the silver may be about 100 .ANG. thick), and the Si.sub.3 N.sub.4 are relatively thicker (e.g. about 320 .ANG. for the undercoat and about 450 .ANG. for the overcoat). The two nichrome layers are adjusted together and therefore have substantially equal thicknesses. It is known in this respect to adjust the thicknesses of these nichrome layers together to improve adhesion by adjusting the relevant parameters in the coater during setup.
FIG. 1 schematically illustrates a typical Airco sputter coater as referenced above, used to produce this known Airco product which is illustrated in FIG. 2. With reference to FIG. 1, Zones 1, 2, 4, and 5 are made up of silicon (Si) tubular targets (t.sub.1-12 and t.sub.19-30) and sputtering is conducted in a 100% N.sub.2 atmosphere. Zone 3 typically employs planar targets "P" and is used to create the three intermediate layers, i.e. Ni:Cr/Ag/Ni:Cr. A 100% argon atmosphere is employed in Zone 3.
While this glass coating achieved good mechanical durability and chemical resistance (i.e. the coating was scratch resistant, wear resistant and chemically stable) and thus achieved an important measure of this characteristic as compared to pyrolytic coatings, its other characteristics in practice, have been found to fall short of the levels of infrared reflectance and visible transmittance characteristics normally desired for low-E architectural glasses. For example, for glass at least 3 mm thick, visible transmittance (Ill. C 10.degree. obs.) for the product shown in FIG. 2 is usually only about 76%, E.sub.h is about 0.20-0.22, and E.sub.h is about 0.14-0.17. Both of these emissivity values are rather high. In addition, sheet resistance (R.sub.s) measures a relatively high 15.8 ohms/sq. (the more acceptable value being less than about 12.0).
Furthermore, this glass of FIG. 2 proved to be non-heat-treatable, so that it could not be bent, tempered, or heat strengthened without adversely affecting the coating or substrate. This is because when subjected to heat-treatment the silver layer becomes discontinuous and voids develop. The result is that emissivity goes up greatly because the silver layer becomes non-uniform; the chemical resistance is very bad; and transmittance goes up greatly.
Thus, while durability was significantly improved and while these coatings also proved to be compatible with conventional sealants, solar management qualities and heat-treatability were less than optimal for many modern architectural purposes.
Using, then, the apparatus and atmosphere of FIG. 1 and by controlling speed and electrical power to the sputtering operation, accordingly, the known Airco process produced a layered system such as that illustrated in prior art FIG. 2. In this FIG. 2, there is shown a glass substrate "G". Such a glass substrate was preferably a sheet of glass of about 2 mm-6 mm thick, usually made by the known float process and of a typical soda-lime-silica composition employed historically in this process. In Zones 1-2, a first undercoat layer 1 consisting essentially of Si.sub.3 N.sub.4 was formed. Its nominal thickness was about 325 .ANG.. Zones 1-2 were conducted in substantially 100% N.sub.2. Next, Zone 3 was employed using a substantially 100% argon atmosphere to first produce a relatively thick (e.g. 7 .ANG.) layer 3 of 80/20 nichrome, followed by a rather discontinuous silver layer 5 whose discontinuity is illustrated by voids 7. In this same Zone 3, there was then applied to the silver another, equally thick (e.g. 7 .ANG.) 80/20 nichrome layer 9. Both nichrome layers were of substantially the same thickness. A topcoat 11 of Si.sub.3 N.sub.4 was then applied in Zones 4-5 with a thickness somewhat greater than that of undercoat 1 due to increased power (e.g. about 450 .ANG. thick). The less than desirable solar management qualities of this glass are mentioned above.
In addition to this Airco layer system illustrated in FIG. 2, other coatings containing silver and/or Ni:Cr as layers for infrared reflectance and other light management purposes have been reported in patent and scientific literature. See, for example, the Fabry-Perot filters and other prior art coatings and techniques disclosed in U.S. Pat. Nos. 3,682,528 and 4,799,745 (and the prior art discussed and/or cited therein). See also the dielectric, metal sandwiches created in numerous patents including, for example, U.S. Pat. Nos. 4,179,181; 3,698,946; 3,978,273; 3,901,997; and 3,889,026 just to name a few. While such other coatings have been known or reported, it is believed that prior to the present invention, none of these prior art disclosures taught or have achieved the ability to employ the highly productive sputter coating process and, at the same time, achieve a glass which not only approaches or equals the durability of pyrolytic coatings, but which also achieves excellent solar management qualities as well.
The popularity of metal and metal oxide coated glasses in architectural and automotive design is also well known. As reported prolifically in patent and other literature, such glasses, usually achieve, through the manipulation of the coating's layering system, fairly acceptable degrees of reflectance, transmittance, emissivity, chemical resistance, and durability, as well as the color desired. See, for example, in this respect, U.S. Pat. Nos. 3,935,351; 4,413,877; 4,462,883; 3,826,728; 3,681,042; 3,798,146; and 4,594,137 just to name a few.
Another Airco prior art coated glass, Airco "Aircool 72 or 76", consists essentially of the following layers from a glass substrate outward: SnO.sub.2 /Al/Ag/Al/SnO.sub.2. While being heat-treatable, these coated glasses are rather soft and lack durability.
In recent years, the popularity of coated glasses has occasioned numerous attempts to achieve a coated glass article which, prior to heat-treatment, can be coated, and which thereafter, can be heat-treated without adversely changing the characteristics of the coating or the glass itself (i.e. the resulting glass article).
One of the reasons for this is, for example, that it can be extremely difficult to achieve a uniform coating on an already bent piece of glass. It is well known that if a flat glass surface can be coated and thereafter bent, much simpler techniques can be used to get a uniform coating than if the glass has been previously bent. This is true for architectural, automotive, and residential glasses.
Certain techniques have been developed in the past for making coated heat-treatable glass articles which may then, and thereafter, be heat-treated by way of tempering, bending, or a technique known as "heat strengthening". Generally speaking, many of these prior coated articles (such as the article of FIG. 2) have suffered from not being heat-treatable at the higher, elevated temperatures necessary to achieve economic bending, tempering and/or heat strengthening (i.e. 1150.degree. F.-1450.degree. F.). In short, such techniques have suffered from a need to keep the temperature at approximately 1100.degree. F. or less in order to achieve heat-treatability without adversely affecting the coating or its substrate. This latter situation; namely the absence of any substantial adverse affect upon the coating or its substrate, herein is ultimately what is meant, then, and in coordinance with the definition given above, by the term "heat-treatable" as used herein.
In this respect, U.S. Pat. No. 5,188,887 discloses certain prior art coating systems which are heat-treatable as that term is defined in this patent because they can be heat-treated successfully at the higher, more elevated temperatures aforesaid, to achieve the desired result despite having gone through tempering, bending or heat strengthening. Generally speaking, these prior art coating compositions find their uniqueness in a layering system which employs as a metallic layer, a high nickel content alloy which, in its preferred form, is an alloy known as Haynes 214, consisting essentially of 75.45% Ni, 4.00% Fe, 16.00% Cr, 0.04% C, 4.50% Al, and 0.01% Y (percentages are by weight). By using a high nickel content alloy, such as Haynes 214, and overcoating it with stoichiometric tin oxide (SnO.sub.2) either alone or with other layers (such as an undercoat of the same stoichiometric tin oxide and/or an intermediate layer of aluminum between the top SnO.sub.2 layer and the high content nickel alloy), it was found that heat-treatability of glass articles at elevated temperatures of from approximately 1150.degree. F.-1450.degree. F. from about 2-30 minutes, could be achieved without substantial degradation of color, mechanical durability, emissivity, reflectance or transmittance. These compositions therefore constituted a significant improvement over prior heat-treatable systems such as those disclosed in the following U.S. Pat. Nos. 4,790,922; 4,816,034; 4,826,525; 4,715,879; and 4,857,094.
In addition to the above disclosures in the aforesaid patents, the Leybold windshield glass system TCC-2000 is also known. This system is generally disclosed in U.S. Pat. No. 5,201,926. In this system, four or five layers of metals and metal oxides are employed to obtain a sputter coated glass which, being somewhat heat-treatable at temperatures up to 1100.degree. F. may be used as a pre-coated glass for making bent or unbent, glass windshields, provided that rapid time limits are placed on the heat-treatment. The layering from glass substrate outward usually includes a first layer of tin oxide, a second layer of nickel/chrome alloy (usually about 80/20), a third layer of silver, a fourth layer of the nickel/chrome alloy, and a fifth layer of tin oxide. In addition to the rather low upper limit on heat-treatment temperature and times, the resultant coatings are rather soft and exhibit such unacceptably low chemical resistance characteristics that they can realistically be used only on the inner surfaces of laminated glass windshields because of their lack of durability. U.S. Pat. No. 5,201,926 further discloses that the upper and/or lower layers in this system may be, in addition to tin oxide, silicon dioxide, aluminum oxide, tantalum oxide, zirconium oxide or mixtures thereof. This patent also states that the silver layer may be silver or a silver alloy of at least 50% by weight silver. The layer thicknesses reported are, respectively (from glass outwardly) 35 nm, 2 nm, 20 nm 2 nm and 35 nm.
In U.S. Pat. No. 5,229,194, which is prior art to the subject invention due to commercial sale more than one year prior to our filing date herein, a significant advance in the heat-treatable sputter coatings is disclosed, even when compared to those disclosed in U.S. Pat. No. 5,188,887. In that invention it was found that unique results in the area of heat-treatable (as that term is defined therein) sputter coated glasses were achievable, particularly when used as "privacy" windows in vehicles, if metallic nickel or a high content metallic nickel alloy layer were surrounded by an undercoat and overcoat of a separate layer of an oxide or nitride of nickel or high content nickel alloy, and a further overcoat of an oxide such as SnO.sub.2, ZnO, TiO.sub.2 or oxide alloys thereof was employed. Silicon is also mentioned as useful for the first overcoat of the metallic nickel-containing layer. The content of the aforesaid U.S. Pat. No. 5,229,194 is hereby incorporated herein by reference.
The above-mentioned layering systems disclosed by U.S. Pat. No. 5,229,194, proved particularly heat-treatable and abrasion resistant. However, while some were found initially to be chemically resistant, certain systems when put into mass production were found not to pass the rather rigorous one hour 5% HCl boil chemical resistance test (discussed above). Their infrared and UV reflectance characteristics were, however, found to be excellent for a wide range of uses. Still further, however, their visible light transmittance values, desirably low for "privacy" window use, nevertheless proved to be too low to be truly useful as glass windows or panels for architectural or residential purposes where high visible light transmittance is required. Thus when production called for the sputter coater to fulfill orders for architectural or residential coated glass after glass sheets for "privacy" windows had been coated, the coater had to be shut down so that a new layering system could be formed. If such a shutdown could be avoided a significant economic advance would be accomplished.
In our commonly owned, co-pending application Ser. No. 07/876,350 filed Apr. 30, 1992, entitled "High Performance, Durable, Low-E Glass and Method of Making Same", there are disclosed certain unique sputter coated layering systems having unique applicability for architectural and residential purposes because of their achievement of not only good chemical and mechanical durability, but their solar management properties as well. These systems are properly deemed "low-E" glasses (coatings) because their hemispherical emissivity (E.sub.h) was generally less than about 0.16 and their normal emissivity (E.sub.n) was generally less than about 0.12. Measured another way their sheet resistance was preferably less than about 10.50 ohms/square. In addition, for normal glass thicknesses (e.g. 2 mm-6 mm) visible light transmittance was preferably about 78% or more (compared to less than about 22-23% in certain preferred embodiments of the aforesaid heat-treatable "privacy" window layer systems of U.S. Pat. No. 5,229,194).
The invention in this aforesaid co-pending application Ser. No. 07/876,350, hereby incorporated herein by reference, achieved its unique low-E, high visible light transmittance values (T&gt;78%, En.sub. &lt;0.12, etc.), along with its good chemical durability (passed the rigorous 5% HCl boil test) and resistance to abrasion, by employing a layer system which, in a first five-layered embodiment, generally comprised (from a glass substrate outwardly) an undercoat layer of Si.sub.3 N.sub.4, a first layer of nickel or nickel alloy (e.g. nichrome), a layer of silver, a second layer of nickel or nickel alloy, and an overcoat layer of Si.sub.3 N.sub.4. In certain other preferred embodiments, the layer system from the glass substrate outwardly consisted essentially of: Si.sub.3 N.sub.4 /Ni:Cr/Ag/Ni:Cr/Ag/Ni:Cr/Si.sub.3 N.sub.4. This seven layer system was found to exhibit somewhat higher durability and scratch resistance characteristics than the above-described five layer system. In each system, however, the preferred Ni:Cr layer was nichrome, i.e. 80/20 by weight Ni/Cr, and in which a substantial portion of the chromium formed as a nitride of Cr because the Ni:Cr layer was formed in a nitrogen-containing atmosphere.
Unfortunately, these durable, low-E, high visible transmittance glass layer systems proved to be non-heat-treatable. It is believed that this non-heat treatability is due to the metallic silver layer(s) during heat-treatment becoming discontinuous due to non-wetting, in this case because the Ni:Cr surrounding layers are insufficient to maintain the continuity of the silver layer(s) during heat-treatment. Thus these otherwise advantageous layer systems could not be used where the layered glass was thereafter to be heat-treated as by tempering, heat strengthening, and bending. Unfortunately, the silver layers were necessary to employ in order to achieve the desired low-E results.
It is to be remembered in this respect that certain architectural, residential, and automotive uses require the coated glass to be tempered, bent, or heat strengthened. Most notably, in architectural settings, the use of heat-treatable "temperable, etc." glasses in conjunction with the non-heat-treatable glass of the aforesaid mentioned Ser. No. 07/876,350 is often required. Therefore, the need arises for production of a heat-treated glass which exhibits characteristics (color, emissivity, sheet resistance, etc.) substantially matching those of the non-heat-treated glass described in aforesaid-mentioned Ser. No. 07/876,350 so that both can be used together; for example in the same building; side-by-side.
In our commonly owned, co-pending application Ser. No. 08/102,281, filed Aug. 5, 1993, hereby incorporated herein by reference, an excellent, heat-treatable glass layering system is disclosed. Such a layering system generally includes multiple family layering systems each of which includes the use of sputter coating targets and atmospheres to form as constituent layers, layers of Si.sub.3 N.sub.4 and Ni/Cr and/or oxides thereof. The coated glass articles described in Ser. No. 08/102,281 after heat-treatment are excellent, but they do not exhibit optical characteristics (color, emissivity, reflectance, etc.) substantially similar or substantially matching those of the unheat-treatable glass described in aforementioned Ser. No. 07/876,350. Nevertheless, and even though it does not meet the need for a system which after heat-treatment substantially matches another glass in unheat-treated form, it can be produced because of its commonality in layers with a minimal change to the sputter coating operation along with the glasses of this invention herein, as well as those of the 876,350 type. This is a significant characteristic and finding of our current invention.
Indeed, an important finding and thus significant aspect of our invention herein, as more fully described below, is the fulfillment of a long felt need to be able to produce with minimal adjustment of the sputter coating operation a flexible range of sputter coating products each being somewhat different and thereby serving to fulfill the varying needs of a diverse range of customers. For example, and as further explained below, in a typical 30 target, Airco sputter coater employing silicon, Ni/Cr, and Ag targets, the subject invention envisions the ability to produce in a single run with simple adjustment to the sputter coater parameters, products for the automotive industry (e.g. coated glass sheet later bent into windshields, etc.) as disclosed in Ser. No. 08/102,281, products for the architectural (building) industry which are untempered as disclosed in Ser. No. 876,350 and products for the architectural (building) and automotive industries which are temperable and bendable, and which optically match those of the '350 type as disclosed by the subject invention.
It is therefore apparent that there exists a need in the art for a sputter coated glass layering system which, after being heat-treated (tempered, bent, etc.) has optical characteristics which substantially match or are substantially similar to those of the low-E non-heat-treatable coated glass of the aforesaid-mentioned co-pending Ser. No. 07/876,350, and preferably which can be manufactured in the same operation as these aforesaid, non-heat-treatable glasses, without shut down of the sputter coating operation. It is a purpose of this invention to fulfill this need in the art as well as other needs which will become apparent to the skilled artisan once given the following disclosure.
As used herein the term "Si.sub.3 N.sub.4 " means the formation of silicon nitride generally and not necessarily a precise stoichiometric silicon nitride -- nor that the layer formed thereof consists entirely of just silicon nitride, since in certain instances the targets employed may be doped with small amounts of such elements as aluminum which then show up in the layer elements or their own nitrides. Thus, the term "Si.sub.3 N.sub.4 " is used herein as a short-hand to designate a layer which consists essentially of the nitride(s) of silicon.
The term "nichrome" in like manner is used herein, in its generic sense to designate a layer which includes some combination of nickel and chromium, at least some of which is in its metallic state, although same may be oxidized. In a similar way the term "silver" means that the layer consists essentially of metallic silver, but may include some other elements in small concentrations that do not adversely affect the performance characteristics of the silver in the system as a whole.